The present invention relates to a method of making an optical fiber coupler by use of a fusionelongation method.
In the fabrication of an optical fiber coupler by use of the fusion-elongation method, a variation in the elongation length of optical fibers, even if very slight, brings about a substantial change in the performance (a branching ratio or isolation, hereinafter identified as the branching ratio) of the optical fiber coupler. To obtain an optical fiber coupler of the desired performance, it is a general practice in the prior art to repeat measurement of the branching ratio upon each occurrence of an extremely slight change in the elongation length until the intended branching ratio is attained. Such a manufacturing method is very timeconsuming for the reasons given below.
Optical fibers must be heated for their elongation; this heating produces a change in the property of the optical fibers, causing the performance of the optical fiber coupler to vary. The optical fiber coupler exhibits its true performance in a heat-free condition; therefore, the performance of the optical fiber coupler must be checked, with the heat source held apart therefrom. In the conventional manufacturing process it is necessary to repeat checking of the performance of the optical fiber coupler being manufactured and the elongation of the optical fibers until the intended performance will have been obtained. This repetitive work consumes an appreciable amount of time in the fabrication of the optical fiber coupler.